Continuation passing style flatten sml

flatten.sml

datatype 'a Tree = 
    Leaf 
  | Branch of {value : 'a, left : 'a Tree, right : 'a Tree}

fun infix_flatten t = case t of
  Leaf => []
| Branch {value, left, right} => let
  val l = infix_flatten left
  val r = infix_flatten right
in 
  l @ (value :: r)
end


val my_tree: int Tree = 
  Branch {
    value = 2, 
    left = Branch { value = 1, left = Leaf, right = Leaf},
    right = Branch { 
      value = 4, 
      left = Branch { value = 3, left = Leaf, right = Leaf}, 
      right = Leaf}
    }

fun infix_flatten2 tree = recur tree (fn x => x)
and recur Leaf k = k []
  | recur (Branch {value, left, right}) k =
      recur left (fn l_ret => 
        recur right (fn r_ret => 
          k (l_ret @ (value :: r_ret))))

;
infix_flatten my_tree
;
infix_flatten2 my_tree


;
fun fact n = if n <= 1 
  then 1 
  else n * fact (n - 1)

fun fact_tail_rec n = loop n 1
and loop n acc = if n <= 1 
  then acc 
  else loop (n-1) (acc * n)

(*

  let (n,acc) = (n,1);
  loop {
    if n <= 1 { break acc }
    else      { (n, acc) = (n-1, acc * n) }
  }

*)

fun fact_tail_rec n = loop n (fn x => x)
and loop n k = if n <= 1
  then k 1
  else loop (n-1) (fn ret => k(n*ret))
;